Our program project focuses on vascular inflammation. This project focuses on Monocyte chemoattractant protein-1 (MCP-1), a pro-inflammatory CC chemokine that plays a pivotal role in recruiting monocytes/macrophages to the arterial wall, mediating both early progression of atherosclerosis and response of the arterial wall to injury. We have demonstrated that accumulation of MCP-1 in SMC is mediated in large part by changes in mRNA stability. Growth agonists, such as PDGF and angiotensin II (Ang II), increase MCP-1 mRNA half-life (t1/2) from 45 min to >3 hr, whereas glucocorticoids decrease the t1/2 to <15 min. Whereas PDGF and Ang II stabilize numerous mRNAs in SMC, the glucocorticoid Dexamethasone (Dex) selectively destabilizes MCP-1 mRNA. The primary goal of this project is to identify the molecules and mechanisms involved in mediating MCP-1 mRNA stability in SMC. We have made substantial progress during the current term of this award, and have demonstrated that Dex-mediated destabilization of MCP-1 mRNA involves a novel mechanism dependent upon the glucocorticoid receptor (GR). Unlike its more typical role as a transcription factor, the GR appears to be part of a degradative complex that specifically binds MCP-1 mRNA. Using an RNA affinity approach, we have identified Y-box binding protein-1 (YB-1), a multifunctional DNA and RNA binding protein with endoribonuclease properties, as a key component of this complex. We believe that we have identified a novel anti-inflammatory pathway mediated by glucocorticoids/GR that involves degradation of MCP-1 mRNA. This renewal will focus on fully elucidating this pathway. We propose 4 aims: 1) Determine the mechanism by which YB-1 and the GR mediate degradation of MCP-1 mRNA in response to Dex. 2) Identify the domains of the GR involved in regulating MCP-1 mRNA stability. 3) Identify other mediators of inflammation that are regulated in SMC by YB-1- and GR-dependent, Dex-mediated mRNA destabilization. 4) Establish that changes in mRNA stability plays an important role in mediating the effect of Dex on MCP-1 mRNA and protein in vivo. These studies may allow development of agents that mimic the potent anti-inflammatory effects of glucocorticoids without inducing their myriad side effects.